Current activity in, and future prospects for, the incorporation of mechanochemically active functional groups (''mechanophores'') into polymers is reviewed. This area of research is treated in the context of two categories. The first category is the development of new chemistry in the service of material science, through the design and synthesis of mechanophores to provide stress-sensing and/or stress-responsive elements in materials. The second category is the reverse-the development of new material architectures that efficiently transmit macroscopic forces to targeted molecules in order to generate chemical reactivity that is inaccessible by other means.
IntroductionThe mechanical forces typical of daily life have the potential to induce dramatic reactivity at the molecular level. The force between an infant's clenched finger and thumb, for example, is more than ten billion times that of the force between atoms in a carbon-carbon bond. Not only are macroscopic forces many orders of magnitude greater than atomic forces, they are also directional, and therefore differ from conventional forms of energy input such as heat and light. In the past four years, several studies have demonstrated that macroscopic mechanical forces can be harnessed at the molecular level, creating a new tool for the organic and materials chemist alike. Broadly, the opportunities in this area can be divided into two categories. First, there is the opportunity to develop new chemistry in the service of material science by designing and synthesizing mechanically activated functional groups (''mechanophores'') and incorporating them as stress-sensing and/or stress-responsive elements in materials. The second opportunity is the complement of the first-the development of new material architectures that efficiently transmit macroscopic forces to targeted molecules and, in so doing, open up a world of chemical reactivity that is inaccessible by other means. We will refer to these as ''chem / mat'' and ''mat / chem'' mechanochemistry, respectively (Fig. 1). The field of mechanochemistry therefore touches on materials chemistry from the point of view of each of its principle progenitors with potential utility in areas ranging from stoichiometric reactivity and catalysis to stress-responsive and selfhealing polymers.We see the greatest opportunities in mechanochemistry arising from situations in which the mechanical force is directly applied to the mechanophore, so that a directional coupling between the vector of applied force and the reaction of interest is possible. The focus of this paper, then, will be on the mechanochemistry of polymers under tension, where the mechanical coupling is most obvious and, therefore, most amenable to the chemist's intuition. Other aspects of mechanochemistry, such as those involved in the milling of crystals, metals, and alloys, 1 are well known and important fields, but they will not be discussed here. A comprehensive review of mechanochemistry in polymers has been published recently by Caruso et al., 2 and it is ...
